Hair loss is a common affliction of humans, the most typical being "alopecia" where males lose scalp hair with age (male pattern baldness). Hair is normally divided into two types, "terminal" and "vellus" hairs. Terminal hair is coarse, pigmented hair which arises from follicles which are developed deep within the dermis. Vellus hair is typically thin, non-pigmented hair which grows from hair follicles which are smaller and located superficially in the dermis. As alopecia progresses, there is a general change from terminal to vellus type hair.
Other changes associated with alopecia are alterations in the growth cycle of hair. Hair typically progresses through three cycles, anagen (active hair growth phase), catagen (transition phase), and telogen (resting phase during which the hair shaft is shed prior to new growth). As baldness progresses, there is a shift in the percentages of hair follicles in each phase, with the majority shifting from anagen to telogen. The size of hair follicles is also known to decrease while the total number remains relatively constant.
A common treatment for the loss of hair has been hair transplantation. Briefly, plugs of skin containing hair are transplanted from areas of the scalp where the hair is growing to bald areas. This procedure is a costly one, in addition to being time-consuming and relatively painful. Other treatments have included ultraviolet radiation and exercise therapy. However, these have not been generally accepted as being effective.
In addition to hair transplants, the most common approach to stimulating hair growth has been in the area of drug therapy. However, the use of drugs in this regard has met with only limited success. One of the most promising compositions for stimulating the growth of hair is disclosed by Upjohn in U.S. Pat. No. 4,596,812, which describes the use of a substance commonly known as "Minoxidil" for treating male pattern baldness. However, while the results generated through the use of Minoxidil have appeared promising, there is still a need in the art for improved compositions capable of stimulating the growth of hair in warm-blooded animals. The present invention fulfills this need, while further providing other related advantages.